Double-sheathed structural cable

ABSTRACT

The structural cable comprises a bundle of load-bearing tendons extending between upper and lower anchoring devices, a first sheath containing the bundle of tendons, and a second sheath arranged around the first sheath, with a gap between the first and second sheaths.

The present invention relates to structural cables used in theconstruction industry. It is applicable, in particular, to stay cablesused for supporting, stiffening or stabilizing structures.

BACKGROUND

Stay cables are widely used to support suspended structures such asbridge decks or roofs. They can also be used to stabilize erectedstructures such as towers or masts.

A typical structure of a stay cable includes a bundle of tendons, forexample wires or strands, housed in a collective plastic sheath. Thesheath protects the metallic tendons of the bundle and provides a smoothappearance of the stay cable.

In certain cases, the sheath is in the form of an integral tube whichextends from the lower anchoring point to the upper anchoring point ofthe stay cable. The tendons are threaded, usually one by one or smallgroups by small groups, into the sheath before anchoring them at bothends. Examples illustrating such technology are described in U.S. Pat.Nos. 5,461,743 and 7,779,499.

In other cases, the sheath is made of segments following each otheralong the cable. Each segment can be made of several sectors assembledaround the bundle of tendons. See, for example, U.S. Pat. No. 5,479,671.

An object of the present invention is to propose another kind of sheathdesign for structural cables.

SUMMARY

The present document discloses a structural cable of a constructionwork. The structural cable comprises:

a bundle of load-bearing tendons extending between upper and loweranchoring devices;

a first sheath containing the bundle of tendons; and

a second sheath arranged around the first sheath, with a gap between thefirst and second sheaths.

The gap between the two concentric sheaths can be advantageously used toinsert some equipment, for example wiring, piping or various kinds ofdevices to provide more functionality in the structural cable, beyondits primary load-bearing function. Visual effects, lightning protection,fire protection can be cited as potential functionality which may beadded thanks to the gap between the first and second sheaths.

In one application, light sources are arranged in the gap between thefirst and second sheaths, the second sheath being at least in partlight-transmissive.

Typically, the second sheath extends over more than 80% of a length ofthe bundle of tendons between the upper and lower anchoring devices.

In an embodiment, the first sheath extends as an integral tubular memberbetween a first end adjacent to the lower anchoring device and a secondend adjacent to the upper anchoring device.

The second sheath can be configured to transmit substantially nolongitudinal effort to the first sheath. Thus, addition of the secondsheath does not alter significantly the mechanical behavior of thestructural cable.

In addition, each segment of the second sheath can be configured totransmit substantially no longitudinal effort to an adjacent segment ofthe second sheath.

An embodiment of the structural cable further comprises at least onerope extending along the bundle of tendons in the gap between the firstand second sheaths, the second sheath being attached to the at least onerope. The rope(s) support(s) the second sheath along the direction ofthe structural cable, such that the efforts between the first and secondsheath are essentially transverse to the direction of the structuralcable.

The second sheath may be attached to the at least one rope usingfasteners each having a first part fixed to a rope and a second partprotruding transversely to the rope and through a wall of the secondsheath, the second part having an end outside the second sheath forreceiving a removable connector.

In an embodiment, the second sheath comprises a plurality of segmentsassembled along the bundle of tendons, each segment being connected tothe at least one rope. A joint member may be disposed between an upperend of a first segment of the second sheath and a lower end of a secondsegment of the second sheath adjacent to the first segment, the jointmember being configured to accommodate a longitudinal displacement ofthe upper end of the first segment relatively to the lower of the secondsegment. For example, the joint member may have an H-shapedcross-section.

Each segment of the second sheath may comprise a plurality of elementsassembled together around the first sheath. For example, the elements ofa segment of the second sheath are assembled together by fitting a maleedge of an element in a female edge of an adjacent element.Alternatively, they can be assembled together using clips holdingopposing edges of adjacent elements.

Advantageously, each segment of the second sheath is at least in partremovable to provide access to the gap between the first and secondsheaths.

In order to minimize transversal movements of the second sheath withrespect to the first sheath, spacing members may be disposed in the gapbetween the first and second sheaths.

BRIEF DESCRIPTION THE DRAWINGS

Other features and advantages of the structural cable disclosed hereinwill become apparent from the following description of non-limitingembodiments, with reference to the appended drawings, in which:

FIG. 1 is a schematic side view of a stay cable;

FIGS. 2-4 are cross-sectional schematic views of structural cablesaccording to embodiments as disclosed herein;

FIG. 5 is an axial sectional view illustrating the assembly of twoadjacent elements of a cable sheath;

FIG. 6 is a perspective view of a double sheath which may be used inembodiments as disclosed herein;

FIGS. 7 and 8 are cross-sectional views of fasteners used to hold asheath on ropes in embodiments as disclosed herein, FIG. 7 being anaxial section along direction VII-VII shown in FIG. 8, and FIG. 8 beinga radial section along direction VIII-VIII shown in FIG. 7; and

FIG. 9 is an longitudinal sectional view illustrating the assembly oftwo adjacent segments of a cable sheath.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a stay cable 10 which is a structural cable extendingbetween two parts 11, 12 of a construction work. The first part 11 is ata higher position than the second part 12. For example, the first part11 belongs to a tower, while the second part 12 belongs to a foundationto stabilize the tower. Alternatively, the first part 11 may belong to apylon, while the second part 12 belongs to some structure suspended fromthe pylon 11.

The construction work typically includes a number of stay cables 10,only one of them being shown in FIG. 1.

The structural cable 10 has a load-bearing part 15 which consists of abundle of tendons disposed parallel to each other (see FIGS. 2-4). Forexample, the bundled tendons may be strands of the same type as used topre-stress concrete structures. Each strand may optionally be protectedby a substance such as grease or wax and individually contained in arespective plastic sheath (not shown).

Each stay cable 10 may have a length of up to several hundred meters,and include a few tens of tendons, as illustrated in FIGS. 2-4.

The load-bearing tendons arc anchored at both ends of the bundle 15using an upper anchoring device 16 mounted on the first part 11 of theconstruction work and a lower anchoring device 17 mounted on the secondpart 12 of the construction work. Between the two anchoring devices 16,17, the bundle of tendons 15 follows a catenary curve due to its ownweight and the tensile force maintained by the anchoring devices. Theanchoring devices 16, 17 are positioned on the first and second parts11, 12 by taking into account the pre-calculated catenary curve of eachstay cable 10.

The bundle of tendons 15 is contained in a first protective sheath 20which is surrounded by a second sheath 22. Both sheaths 20, 22 aretypically made of plastic material. The materials of the two sheaths maybe different from each other.

The first and second sheaths 20, 22 are spaced apart from each other, sothat there is a gap between them. In the example shown, both sheaths 20,22 have a circular cross-section and are arranged substantiallyconcentric to each other along the bundle of tendons 15. Therefore, thecross-section of the gap has an annular shape.

In order to facilitate the design and the mounting of the structuralcable 10, the first sheath 20 may consist of an integral tubular memberextending between a first end adjacent to the lower anchoring device 17and a second end adjacent to the upper anchoring device 16. The bundleof tendons 15 and the first sheath 20 can then be installed according toa conventional method, for example as described in U.S. Pat. Nos.5,461,743 or 7,779,499.

In the example illustrated in FIG. 1, the first end of the first sheath20 bears on a guide tube 25 through which the bundle of tendons 15passes near the lower anchoring device 17, while the second end of thefirst sheath 20 penetrates into another tube 26 disposed on the firstpart 11 of the construction work, through which the upper end of thebundle of tendons 15 passes to reach the upper anchoring device 16. Thesecond end of the first sheath 20 is not connected to the tube 26, sothat it can slide therein when the tendons 15 and the sheath 20 undergodifferent expansion or contraction on account of the thermal expansioncoefficients of their materials. The arrangement prevents run off waterfrom flowing inside the first sheath 20.

The weight of the plastic sheath 20 is taken up by some transverseeffort on the bundle of tendons 15, and mainly by an axial effort on theguide tube 25. Alternatively, the first sheath 20 may be suspended fromthe first part 11 of the construction work near the upper anchoringdevice 16, with a buffering arrangement near the lower end of the staycable to accommodate for the different thermal expansion behaviors.

The second sheath 22 is mounted around the first sheath 20 so as to be,to a large extent, mechanically independent from the first sheath 20. Inother words, the second sheath 22 is configured to transmitsubstantially no longitudinal effort to the first sheath 20.

Such independence of the second sheath 22 can be achieved by attachingthe second sheath 22 to one or more ropes 30 extending along the bundleof tendons 15 in the gap between the first and second sheaths 20, 22,using an arrangement as illustrated in FIGS. 6-8.

FIG. 6 shows the two concentric sheaths 20, 22 with a pair of ropes 30arranged in the gap at diametrically opposed positions. It will beappreciated that there can be only one rope, or more than two ropes.Each rope 30 can be made of metallic wires and have its two endsconnected to the first and second parts 11, 12 of the construction workusing respective anchoring devices (not shown).

The wire ropes 30 are arranged near the inner surface of the outersheath 22, to which they are attached via fasteners 32 distributed alongthe length of the stay cable. Each fastener 32 (FIGS. 7-8) has a sleevepart 33 in which the wire rope 30 is threaded and having swaged ends 34for fixing the sleeve part 33 to the rope 30. The fastener 32 alsoincludes a rod part 35 protruding transversely from the sleeve part 33and the rope 30. To attach the second sheath 22 to the wire rope 30, therod part 35 is inserted in a hole formed in the wall of the secondsheath 22, and a removable connector 36 is received at the end of therod part 35 outside the sheath 22. In the example shown, the removableconnector 36 is a circlip engaging an annular groove of the rod part 35,a washer 37 being placed between the wall of the second sheath 22 andthe circlip 36. Other connectors such as locking pins can be used.

The wire ropes 30 and the fasteners 32 hold each segment of the secondsheath 22 such that the weight of each segment of the second sheath 22does not translate into longitudinal efforts applied on the first sheath20 or the bundle of tendons 15, and is not applied on an adjacentsegment of the second sheath 22.

FIG. 6 shows one segment of the second sheath 22. In an embodiment, aplurality of such segments are assembled along the structural cable 10.Each segment, having a length of 3 to 10 m, for example, is connected tothe wire ropes 30 stretched between the two sheaths 20, 22 by means offasteners 32.

Joint members 40 are disposed between the segments of the second sheath22 to ensure their proper alignment while allowing some relativelongitudinal displacement of the axial ends of adjacent segments.

A possible configuration of such a joint member 40 is shown in FIG. 9.In this case, the joint member 40 has an annular shape with a diameteradapted to that of the second sheath 22, and an H-shaped cross-section.The H-shaped joint member 40 has two opposite annular openings, onereceiving the upper end of a first segment of the second sheath 22, andthe other one receiving the lower end of a second segment of the secondsheath adjacent to the first segment.

When installing the second sheath 22, a spacing d is left between theaxial ends of the adjacent segments. The spacing d and the axial lengthD of the joint member 40 are selected depending on the length of thesheath segments and the thermal expansion coefficients of the plasticmaterial of the sheath 22 and of the metal of the wire rope 30, so thatthe axial ends of the adjacent segments remain held in the openings ofthe H-shaped joint member 40 when the stay cable undergoes temperaturevariation in the relevant range for the construction work. Thetemperature range is typically 50° C. or more.

In another configuration, the upper end of a sheath segment overlaps thelower end of the sheath segment located just above it, for example asdescribed in U.S. Pat. No. 5,479,671. Thus, a tulip-shaped overlap jointis formed between the two adjacent segments. In case the second sheath22 is not flexible or ductile enough, a space is provided between thefemale and male parts of this tulip-shaped overlap joint to allow sometelescoping movement of the two sheath segments so as to accept somethermal expansion and rotation of the sheath segments.

A segment of the second sheath 22 may consist of an integral piece oftube, as illustrated in FIG. 2.

Alternatively, the segment may consist of a plurality of sector-shapedelements assembled together around the first sheath 20. In theillustration of FIG. 3, there are four elements 22 a, 22 b, 22 c, 22 deach having a cross-section in the form of a 90° sector. In theillustration of FIG. 4, there are two elements 22A, 22B each having across-section in the form of a 180° sector. Those elements are assembledtogether by fitting the male edge 42 of an element in the female edge 43of an adjacent element.

Another way of assembling sheath elements is illustrated in FIG. 5.Here, the elements 22A, 22B of a segment of the second sheath 22 areassembled using clips 45 holding opposing edges of adjacent elements.

In the example of FIG. 5, each sheath element 22A, 22B has longitudinalgrooves 46 next to its longitudinal edges, one on each face. The clip 45has a generally H-shaped cross-section, with each half fitted on thelongitudinal edge of a sheath element 22A, 22B. The profile of the clip45 also has inner dogs or ribs 47 engaging the longitudinal grooves 46of the sheath element 22A, 22B to secure the elements in position.

As shown in FIGS. 3 and 4, spacing members 50 may be disposed in the gapbetween the first and second sheaths 20, 22, in order to limittransversal movement of the second sheath 22 with respect to the firstsheath 20. The spacing members 50 may have elastic or viscoelasticproperties. They can be fixed to the first sheath 20, the second sheath22, or both.

When the designer of the construction work takes advantage of the gapbetween the first and second sheaths 20, 22 to add some functionalelement to the stay cable, that functional element may, if appropriate,play the role of a spacing member 50.

In the embodiment illustrated by FIG. 6, the second sheath 22 is made ofa transparent plastic material, and light sources are disposed in thegap between the first and second sheaths 20, 22. The light sources are,for example, light-emitting diodes (LEDs) arranged along strips 50. Eachstrip 50, mounted on a profile 51 fixed on the outside of the firstsheath 20, plays the role of a spacing member.

Making the second sheath 22 of a transparent plastic material offers avariety of options to add architectural features to the cabledsuspension of the construction work. Ornamental or colored patterns canbe inserted to give a distinctive appearance to the construction work.In particular, light patterns can be created using LEDs or other kindsof sources.

More generally, the second sheath 22 may be made of a light-transmissivematerial, e.g. transparent, translucent, with or without color filters,etc. The light-transmissive property can be provided on the wholesurface of the second sheath 22, or only on part of it, for examplewhere rows of light sources are disposed.

If it is desired for maintenance purposes, the annular gap between thefirst and second sheaths 20, 22 can be made accessible from the outsideby the arrangement of the segments making up the second sheath 22. Theelements forming the sheath segments are removable to provide the accessto the gap. This can be done by removing the connectors 36 of thefasteners 32 (FIGS. 7-8) and using flexibility of the materials of thejoint members 40 (FIG. 9) and/or clips 45 (FIG. 5) to extract theelement. The joint members 40 and/or clips 45 may have a removable parton the outside to facilitate dismounting of a sheath element whenneeded.

The fact that the second sheath 22 is made independent of the firstsheath 20 and the bundle of tendons 15 regarding longitudinal effortsensures that an element of the second sheath 22 can be temporarilyremoved to have access to the gap without causing problems.

During the lifetime of the construction work, maintenance or replacementof part or all of the structural tendons within the bundle 15 and thefirst sheath 20 may have to be undertaken. When the proposed doublesheath arrangement is used, such maintenance or replacement can becarried out without any interference with the second sheath 22 andassociated equipment.

In some cases, the second sheath 22 may cover only a portion of therunning part of the structural cable 10. However, it will generally bepreferred to install it over the whole running part. It is not practicalto have the second sheath 22 extended all the way to the anchoringdevices 16, 17. Also, the second sheath 22 may have to be interrupted atplaces if some of the cables are connected together by vibration dampingdevices as described, e.g., in U.S. Pat. No. 7,631,384 or application US2015/113744 A1. Where such damping devices are provided, adjacent sheathsegments are spaced apart at the level of their fixing collars, and theropes 30 should pass through or around the collars to properly hold thesecond sheath 22. Overall, the cable portions not covered by the secondsheath 22 are minimized. Typically, the second sheath 22 extends overmore than 80% of the length of the bundle of tendons 15 between theanchoring devices 16, 17, or even more than 90% for long stay cables.

In the configuration diagrammatically illustrated by FIG. 1, the upperend of the second sheath 22 is located within the upper tube 26 mountedon the first part 11 of the construction work, so that it is not visibleand run off water is prevented from flowing inside the second sheath 22.

To ensure good dynamic properties of the stay cable 10, it is preferableto give the second sheath 22 a regular profile, typically with acircular cross-section. The second sheath 22 may also be provided withspecific surface structure, known in the art, e.g. double helical ribs,to improve its behavior in the presence of a combined action of rain andwind.

It will be appreciated that the embodiments described above areillustrative of the invention disclosed herein and that variousmodifications can be made without departing from the scope as defined inthe appended claims.

For example, the invention is applicable to structural cables other thanstay cables.

1-7. (canceled)
 8. A structural cable of a construction work, thestructural cable comprising: a bundle of load-bearing tendons extendingbetween upper and lower anchoring devices, the outer sheath being madeof at least one segment having a cross-section formed of an integralpiece of tube; an outer sheath containing the bundle of tendons; andlight sources arranged within a cross-sectional profile of the outersheath so as to radiate light out of the structural cable.
 9. Thestructural cable as claimed in claim 8, wherein the sheath extends overmore than 80% of a length of the bundle of tendons between the upper andlower anchoring devices.
 10. The structural cable as claimed in claim 8,further comprising an inner sheath concentrically arranged with theouter sheath, wherein the bundle of tendons is inside the inner sheath,wherein the outer sheath is at least in part light-transmissive, andwherein the light sources are arranged in a gap between the inner andouter sheaths.
 11. The structural cable as claimed in claim 10, whereinthe outer sheath is configured to transmit substantially no longitudinaleffort to the inner sheath.
 12. The structural cable as claimed in claim10, further comprising at least one rope extending along the bundle oftendons in the gap between the inner and outer sheaths, wherein theouter sheath is attached to the at least one rope.
 13. The structuralcable as claimed in claim 12, wherein the outer sheath comprises aplurality of segments assembled along the bundle of tendons, eachsegment being connected to the at least one rope.
 14. The structuralcable as claimed in claim 13, wherein each segment of the outer sheathis configured to transmit substantially no longitudinal effort to anadjacent segment of the outer sheath.
 15. The structural cable asclaimed in claim 13, further comprising a joint member disposed betweenan upper end of a first segment of the second sheath and a lower end ofa second segment of the second sheath adjacent to the first segment,wherein the joint member is configured to accommodate a longitudinaldisplacement of the upper end of the first segment relatively to thelower of the second segment.
 16. The structural cable as claimed inclaim 8, wherein the outer sheath has transparent portions where thelight sources are disposed.
 17. The structural cable as claimed in claim8, wherein the profile of the outer sheath has a circular cross-section.18. The structural cable as claimed in claim 8, wherein the outer sheathis provided with a surface structure to improve a behavior of thestructural cable in the presence of a combined action of rain and wind.